Magnetic resonance imaging system

Abstract: This invention relates generally to the field of Magnetic Resonance Imaging (MRI) systems for generating diagnostic images of a patient's internal organs and more particularly, this invention relates to improved MRI systems with decreased interference between the magnetic field used for producing diagnostic images and the magnetic fields generated by the electric motors (35,86) used for driving the pistons of the contrast media injectors. Additionally, the system employs an improved communication link (22,26) between an externally located system controller (12) and the injection head control (38) unit located within the electromagnetic isolation barrier (18) which defines the magnetic imaging room.

Description: This invention relates to a magnetic resonance imaging (MRI) system for generating diagnostic images of a patient's internal organs. It has become recognized that MRI systems require isolation from external sources of electromagnetic fields, if optimum image quality is to be obtained from MRI diagnostic procedures. Conventional MRI systems have typically employed some form of electromagnetic isolation chamber which is generally a room enclosed by copper sheeting or conductive mesh material that isolates the room from undesirable sources of electromagnetic radiation and the electromagnetic noise inherent in the atmosphere. In order to realize the full benefit of the shielded room, these systems employ a controller for the contrast media injector portion of the system which is isolated from the media injector as for example disclosed in "In Vitro Evaluation of a Mechanical Injector for Infusion of Magnetic Resonanse Contrast Media", Vol 26 Nuember 8, pages 748-751, Investigative Radiology. Such isolation is effected to prevent undesirable electromagnetic radiation generated by the system controller from interfering with the signals used to create the magnetic resonance images. The external, isolated location of the system controller creates various problems associated with the installation and operation of these systems. One such problem is the need to provide a communications link between the externally located controller and the contrast media injectors, without introducing extraneous electromagnetic radiation. That is, there is a need to provide electrical power supply lines for operation of the contrast media injectors and the injector control circuitry while maintaining the integrity of the electromagnetic shield. Previous attempts to solve these problems included drilling holes in the wall of the electromagnetic shield for inserting the necessary lines or, alternatively, laying the lines under a shielded floor of the imaging room. These alternatives have proven to be less than optimum, since spurious radiation arose from the presence of the various supply cables within the shielded imaging suite. Additionally. MRI systems which employed these solutions required substantial site dedication and were therefore not very portable. Accordingly, it is an object of the present invention to provide an improved magnetic resonance imaging contrast media delivery system having decreased interference between the magnetic field used to obtain the magnetic resonance image and the magnetic fields created by ancillary equipment. This object is solved in a magnetic resonance imaging system for generating diagnostic images of a patient's internal organs according to claim 1. The system has an improved communication link between an externally located system controller and the injection head control unit which is located within the electromagnetic isolation barrier fo the magnetic imaging suite. The system exhibits decreased interference between the magnetic field used for producing diagnostic images and spurious magnetic fields created by ancillary equipment. The invention comprises an improved magnetic resonance imaging system which decreases the amount of electromagnetic interference that has heretofore been found within a MRI isolation suite while increasing the portability and ease of system installation. Further preferred embodiments of the invention and the features thereof are given in the appended subclaims. Preferred embodiments of the invention will now be described in detail in conjunction with the accompanying drawings in which FIG. 1 is a block diagram outlining the functional design of the system; and FIG. 2 is a diagram illustrating the system of the present invention. The system includes a master controller located externally of the shielded imaging room within which a contrast media injection head and a separate injection control unit are located. The system controller communicates with the head control unit via external and internal transceivers which form a communications link for traversing the electromagnetic isolation barrier of the imaging room. This communication link is made through a window in the isolation room barrier. These windows are typically in the form of a glass laminate containing a conductive wire mesh, or alternatively, a window that is coated with a thin sheet of conductive material such as gold to maintain the shielding characteristics of the isolation room. The communications link consists of electromagnetic transceivers which operate in a frequency range which permeates the window while maintaining the integrity of the isolation barrier. Infrared or electromagnetic energy in the visual range provide the best results. The system also incorporates a contrast media injection unit located within the shielded room which comprises separate contrast media injector head and injection head control unit. The contrast media injection head, and specifically the syringe pistons are located in close proximity to the patient and consequently are located within the powerful magnetic field used to generate the magnetic resonance image. The head control unit which controls operation of the injector head is located from 3 to 5 m (10-15 feet) away from the injector head control unit. The head control unit incorporates electric motors to control and to operate the pistons of syringes used for the injection of patients. A non-rigid operating drive connects the electric motors and control unit to the syringe pistons located on the injection head. In a preferred form, the drive connection can be by way of flexible shafts. Each flexible drive shaft forms a mechanical link between an electric motor located on the head control unit and a piston of the syringes on the injector head. Alternatively, a hydraulic system could be used to control the piston of the injector head. In the preferred embodiment, the flexible drive shaft is manufactured from a non-ferrous metal such as hard brass. The distancing of the head control unit and drive motors from the injector head decreases the adverse effects that the imaging magnetic field has on the electric motors of the injectors and conversely, the adverse effects of spurious electromagnetic radiation arising from operating of the electric motors used to control and operate the contrast media injectors is also reduced significantly. Figure 1 illustrates a magnetic resonance imaging system and is shown generally at 10. The MRI system includes a system controller 12 which incorporates a computer 14 and a battery charging unit 16. The system controller 12 is located externally of the imaging room 17, the imaging room being shielded from electromagnetic interference by a shield 18. Isolation can be achieved by completely enclosing the room with copper sheet material or some other suitable, conductive layer such as wire mesh. Communication line 20 connects the system controller 12 with an external infrared / optical communications transceiver 22. The shielded imaging room 17 also incorporates a patient viewing window 24 in the shield 18 which allows an observer to view the room without breaching the electromagnetic shield 18. The window 24 can be formed by sandwiching a wire mesh material (not shown) between sheets of glass or coating the window with a thin coating of conductive material such as gold (not shown) to maintain the continuity of the electromagnetic shield 18. An infrared / optical communications transceiver 26 is positioned internally of the imaging room 17 at the viewing window 24 opposite the external communications transceiver 22 such that the internal and external communications transceivers communicate with each other through the viewing window with no breach of the electromagnetic shield. A communications link 28 located within the shielded area connects the internal infrared / optical transceiver with a contrast media injection control unit 30. The injection control unit 30 is powered advantageously by rechargeable battery 32. The injection control unit 30 also incorporates control circuitry which controls electric motors 35, 36 which are also located within the injection control unit. The injection control unit is contained within an electromagnetic shield 37 to prevent the undesired electromagnetic radiation generated by the electric motors from interfering with the magnetic field used to generate the magnetic resonance image. The injection control unit 30 is separated from the injection head unit 38 by as great a distance as possible. In the preferred embodiment, this is typically 3 to 5 m (ten to fifteen feet). The injection head unit must be located in close proximity to the patient in order to decrease the distance that the contrast media fluid must travel from the contrast media injectors. The injection head unit 38 includes contrast media injection syringe and piston units 40, 42. The syringes 40, 42 are connected to the electric motors in the injection control unit by flexible mechanical drive shafts 44, 46, respectively. The drive shafts are made from a nonferrous metal such as hard brass. The separation of the electric motors from the injection head, as well as the additional electromagnetic shielding, results in improved system performance and overall resulting image quality. Additionally, the use of an infrared / optical communications link results in a system which is both portable and easy to use.

Claims: A magnetic resonance imaging system comprising: a) a room shielded from electromagnetic interference, which includes a viewing window, the viewing window maintaining the shielding characteristics of the room; b) a system controller external to the shielded room; c) a patient injection apparatus within the shielded room and including injection apparatus control means; and d) a wireless communications link between the system controller and the injection apparatus control means made through said window. The magnetic resonance imaging system of claim 1, wherein the communications link transmits and receives electromagnetic radiation through the viewing window. The magnetic resonance imaging system of claim 2, wherein the communications link transmits and receives infrared electromagnetic energy. The magnetic resonance imaging system of claim 2, wherein the communications link transmits and receives electromagnetic energy in the visual range. The magnetic resonance imaging system of claims 1, wherein the injection apparatus control means is powered by a rechargeable battery. The magnetic resonance imaging system of claim 1, wherein the injection apparatus includes two syringe and piston units the syringes of which are connected to electric motors in the injection apparatus control means by non-rigid drive connections.

Inventors: MANLEY JON E, STULEN JOHN, UBER ARTHUR E, WADDELL SEID, MANLEY, JON E., STULEN, JOHN, UBER, ARTHUR E., WADDELL, SEID, UBER, ARTHUR E., III
Applicants: MEDRAD INC, MEDRAD INC.
Application year: 1994
Main classification: G01R33
IPC codes: A61M5, G01R33, A61B5